Truly Tasteless Jokes by Blanche Knott
I grew up on this series of books. Contained in these pages are some of the best and most famous jokes ever told. At camp, it was precious contraband, akin to a porn collection, for a bunch of 13-year olds. I would read the same jokes over and over. We would skip from page to page, subject to subject, and laugh our asses off. This is the book to buy if you don't have a go-to joke. Pick a joke, any joke, and practice. Ideally, you will have this joke perfected so that when you are put on the spot, you can deliver it. It can't be too dirty or too clean, or maybe you can remember a bunch of them.